Substrates for optical cards, process for preparing substrates for optical cards, optical cards and apparatus for recording and reproducing information on optical cards

ABSTRACT

A substrate for an optical card having tracking grooves in a stripe form formed on the surface of an extrusion-molded thermoplastic resin sheet is characterized in that the direction of the tracking grooves is in parallel to the extrusion direction of the thermoplastic resin sheet, and the recording or reproduction using the optical card is characterized by that the optical card is bent and reciprocally moved along the direction of tracking grooves.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to substrates for optical recording media forrecording and reproducing information by light, such as laser beam,etc., particularly substrates for optical cards and to a process forpreparing the same.

2. Related Background Art

In optical recording media, information is recorded by forming pits inthe recording layer by irradiation of laser beam with or without thesimultaneous application of an appropriate external energy or force, forexample, heat or magnetic force, where the following types are known:

1. Pit-forming type using a recording layer of Te, Te-C, etc.,

2. Rim-forming type using an organic pigment,

3. Phase change type by inorganic multicomponent compounds such asGe-Sn-Te, TeO-SnGe, etc., and

4. Magneto-optical type which records by changing the spin direction byusing multi-comonent compounds such as Tb-Fe-Co, Tb-Fe-Gd-Co, etc., andconducting photoirradiation while applying a magnetic field thereto.

The pits formed in the recording layer by any of these procedures areexposed to a substantially weaker laser beam than the recording beam,and the reflected light from the recording layer is detected todetermine the presence or absence of pits and reproduce the recordedinformation.

In such an optical recording medium, as shown in FIG. 2B, usually arecording layer 62 is formed on a transparent plastic substrate 28, andirradiation of a laser beam or receiving of reflected light forrecording or reproduction is carried out through the substrate 28.

Generally, irradiation of a laser beam and receiving of reflected lightare carried out together with a polarizing beam splitter (PBS) 22 and aquarter wave plate (QWP) 23 in order to eliminate the return light ofthe laser beam and efficiently receive the reflected light, as shown inFIG. 2A.

That is, the straight polarized beam emitted from a semiconductor laser21 passes through PBS 22 and then passes through QWP 23 to be convertedto a circular polarized beam, which is focused to a spot, about 1 μm indiameter, through a focusing lens 24 to enter the substrate 28 andirradiate the recording layer 62. Then, the light reflected on therecording layer 62 passes again through QWP 23 to be converted again tothe straight polarized beam, which enters PBS 22. At that time, as thereflected light differs by 90° in the polarizing plane from the incidentlight, the reflected light can not pass PBS, and is reflected by PBS toreach a photo detector (PD) 25.

However, as the reproduction of information is carried out with thereflected light from the recording layer through the substrate, asmentioned above, if the substrate 28 has a refractivity, the reflectedlight is not converted to the straight polarized beam exactly by 90°difference in the polarizing plane from the incident light when thereflected light passes through QWP, and a portion of the reflected lightis not reflected by PBS but passes through PBS, and the not-reflectedlight returns to the semiconductor laser, causing noise on the lightsource, and the S/N ratio lowers due to the decrease in the reflectedlight quantity which reaches PD.

Double refraction of the substrate occurs owing to the photoelasticitycoefficient C peculiar to a material multiplied by a residual mechanicalstress difference per se, as shown by the following formula (1):

    Double refraction:(BR)[nm]=(λδ/2)·C·t (δ.sub.1 -δ.sub.2)                            (1)

where

δ: retardation

λ: wavelength

C : photoelasticity coefficient

δ₁ -δ₂ =stress difference

As a material for substrate 28 for information recording medium, such asoptical disk, etc. polycarbonate is regarded as promising owing to lowhydroscopicity, high heat resistance and distinguished moldability.However, polycarbonate resin has so high a photoelasticity coefficientthat double refraction is very liable to occur. Thus, in order tosuppress double refraction when a substrate for optical disk havingpreformats such as track grooves or pits is prepared by molding thepolycarbonate resin, processes and conditions for molding thepolycarbonate to prevent occurrences of residual strains as much aspossible, have been investigated, and polycarbonate substrates with lowdouble refraction have been prepared.

An optical card, is an optical recording medium whose recording andreproduction of information are conducted by relative reciprocalmovements to a light beam for recording and reproduction. It ispreferably bent to a slight degree with rollers 27 to eliminatevibration and slipping of the optical card when the optical card issubjected to reciprocal movement in the direction F traversing withrespect to the light source 21 by a driving roller 26 during therecording and reproduction as shown in FIGS. 2A and 2B. However, whenthe polycarbonate substrate is bent in such a manner as above, a doublerefraction occurs or increases on the substrate 28, resulting inlowering of S/N ratio of the signal.

SUMMARY OF THE INVENTION

The present invention has been established to solve the foregoingproblems of prior art.

An object of the present invention is to provide a substrate for opticalcards with less occurrence of double refraction when an external forceis applied to the substrate during the recording and reproduction, and aprocess for preparing that substrate.

Another object of the present invention is to provide an optical cardcapable of recording and/or reproducing signals in a high S/N ratio evenif an external force is applied to the card during the recording and/orreproduction.

Other object of the present invention is to provide an apparatus forrecording an optical card, which is capable of recording informationwith a high S/N ratio on the optical card.

A further object of the present invention is to provide an apparatus forreproducing an optical card, which is capable of reproducing informationrecorded on the optical card with a high S/N ratio.

Still further object of the present invention is to provide a processfor preparing substrates for the optical cards having exactlytransferred preformats with less occurrence of double refraction even ifan external force is applied to the optical cards during the recordingand reproduction.

Still further object of the present invention is to provide a processfor recording information on an optical card with a high S/N ratio.

Still further object of the present invention is to provide a processfor reproducing information recorded on an optical card with a high S/Nratio.

The present substrate for an optical card comprises an extrusion-moldedthermoplastic resin sheet and tracking grooves in a stripe form formedon the surface of the thermoplastic resin sheet, and the direction ofthe tracking grooves are in parallel to the extrusion direction of thethermoplastic resin sheet.

Furthermore, the present process for preparing a substrate for anoptical card is characterized by molding tracking grooves in a stripeform on a surface of the extrusion-molded thermoplastic resin sheet by astamper so that the direction of the tracking grooves is parallel to theextrusion direction of the thermoplastic resin sheet.

Furthermore, the present optical card comprises (i) a substrate for anoptical card, having stripy tracking grooves on the surface of theextrusion-molded thermoplastic resin sheet, wherein the extrusiondirection of the thermoplastic resin sheet is parallel to the directionof the tracking grooves, (ii) at least one of a recording layer and areflection layer and (iii) a protective substrate, all laid upon oneanother in this order.

Furthermore, the present recording apparatus for recording informationon an optical card comprises a substrate prepared from anextrusion-molded thermoplastic resin sheet, a recording layer, or both arecording layer and a reflecting layer, and a protective substrate, alllaid upon one another in this order. The present recording apparatuscomprises (i) a unit including light source for focusing a light beam onthe recording layer surface of the optical card through the substrate;(ii) a unit for reciprocally moving the optical card the focused lightbeam along the extrusion direction of the thermoplastic resin sheet;(iii) a unit for modulating the intensity of the light beam according toinformation to be recorded; and characteristically (iv) a means forbending the optical card toward the light source along the extrusiondirection of the thermoplastic resin sheet.

Furthermore, the present reproducing apparatus is for reproducinginformation recorded on an optical card, comprising a substrate preparedfrom an extrusion-molded thermoplastic resin sheet, at least one of arecording layer and a reflecting layer, and a protective substrate, alllaid upon one another in this order, wherein information is given in anoptically detectable pit form on the recording layer or the substratesor both. The present recording apparatus comprises (i) a unit includinga light source for focusing light on the recording layer surface or thereflecting layer surface of the optical card through the substrate; (ii)a unit for reciprocally moving the optical card along in the extrusiondirection of the thermoplastic resin sheet; (iii) a unit for detectingthe reflected light from the recording layer or the reflecting layer;and characteristically, (iv) a means for bending the optical card towardthe light source along the extrusion direction of the thermoplasticresin sheet.

Furthermore, the present process for recording information on an opticalcard comprising extrusion-molded thermoplastic resin sheet substrate,the recording layer or both of the recording layer and a reflectinglayer, and a protective substrate, all laid upon one another in thisorder, comprises focusing the modulated recording light through thesubstrate on the surface of the recording layer to cause an opticallydetectable change in the recording layer, wherein the recording ofinformation is carried out with the optical card bent towards a lightsource of the recording light along extrusion direction of thethermoplastic resin sheet.

Furthermore, the present process for reproducing recorded information inan optical card comprising an extrusion-molded thermoplastic resin sheetsubstrate, at least one of a recording layer and a reflecting layer, anda protective substrate, and having information given in an opticallydetectable pit form on the recording layer and/or the substrate,comprises focusing the reproducing light on a recording layer or areflecting layer through the substrate of the optical card, whereinreproduction of the information is carried out with the optical cardbent towards a light source of the reproducing light along the extrusiondirection of the thermoplastic resin sheet.

Furthermore, the present apparatus for recording information on anoptical card comprising (i) an extrusion-molded thermoplastic resinsheet substrate, wherein tracking grooves in a stripe form are formed onthe surface of the resin sheet, and the extrusion direction of thethermoplastic resin sheet is parallel to the direction of the trackinggrooves, (ii) a recording layer and/or a reflecting layer, and (iii) aprotective substrate, all laid upon one another in this order, comprisesa unit including a light source for focusing a light beam on therecording layer surface in the optical card through the substrate; aunit for reciprocally moving the optical card under the focused lightbeam along the direction of the tracking grooves; a unit for modulatingthe intensity of the light beam according to the information to berecorded; and characteristically a means for bending the optical cardtowards or backwards the light source along the direction of thetracking grooves.

Furthermore, the present apparatus for reproducing information recordedon an optical card comprising (i) an extrusion-molded thermoplasticresin sheet substrate having tracking grooves in a stripe form on thesurface of the resin sheet, wherein the extrusion direction of thethermoplastic resin sheet is parallel to the direction of the trackinggrooves, (ii) at least one of a recording layer and a reflecting layer,and (iii) a protective substrate, where information is given in a pitform on the recording layer and/or the substrate, comprises, a unitincluding a light source for focusing a light beam on the recordinglayer surface or the reflecting layer surface in the optical cardthrough the substrate; a unit for reciprocally moving the optical cardunder the focused light beam along the direction of the trackinggrooves; a unit for detecting the reflected light from the recordinglayer or the reflecting layer; and characteristically a means forbending the optical card towards or backwards the light source along thedirection of the tracking grooves.

The present inventors have found that, when resin sheets are prepared byextrusion molding of thermoplastic resin bent in parallel to theextrusion direction of the resin sheets, the occurrence of doublerefraction is quite low in the resin sheets and have thus accomplishedthe present invention.

It is not clear why the occurrence of double refraction can besuppressed so low when the resin sheets are bent in the extrusiondirection, but it seems due to the following facts.

That is, even if a thermoplastic resin sheet is a polycarbonate resin inamorphous state having a low double refraction, microscopically the longchains of polycarbonate resin are oriented in a certain direction. Thelong chains of polycarbonate resin have a spiral structure, and when thepolycarbonate resin sheet is bent in a direction deviated from theorientation direction of long chains of polycarbonate resin the spiralstructure of long chain should be distorted. Therefore to cause bendingto a given degree, it is necessary to apply a large force thereto. Thatis, the term "stress difference" (δ₁ -δ₂) in the foregoing equation (1)becomes larger, resulting in an increase in the double refraction. Onthe other hand, when the polycarbonate resin sheet is bent in a paralleldirection to the orientation direction of long chains, only theextension and contraction of the spiral structure of long chains arerequired, and thus a relatively small force can make bending to the samedegree as above. As a result, the term "stress difference" in theequation (1) becomes smaller, resulting in a decrease in the doublerefraction. In the case of extrusion molding, the resin extrusiondirection is identical with the orientation of long chains of the resin,and thus it seems that occurrence of double refraction is less when theresin sheet is curved in the extrusion direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing one embodiment of a process forpreparing a substrate for an optical card according to the presentinvention.

FIGS. 2A and 2B are schematic views of an apparatus for recording andreproducing an optical card, where FIG. 2A is a oblique view and FIG. 2Bis an enlarged cross-sectional view in part of an optical card.

FIG. 3 is a schematic view showing another embodiment of a process forpreparing a substrate for an optical card according to the presentinvention.

FIG. 4 shows the predetermined size of preformats on a substrate for anoptical card.

FIG. 5 is a schematic view showing other embodiment of a process forpreparing a substrate for an optical card according to the presentinvention.

FIG. 6 is a cross-sectional view in a tracking groove-transversingdirection of an optical card according to the present invention.

FIG. 7 is a schematic view of an apparatus for recording and reproducinginformation on an optical card according to the present invention.

FIGS. 8(A) and 8(B) illustrate Example 1 and Comparative Examples 1 and2, where FIG. 8(A) is a graph showing the quantity of double refractionwhen a substrate for an optical card is held in a flat state and when itis bent, and FIG. 8(B) shows positions of measurements of the quantityof double refraction of a substrate for an optical card.

FIG. 9 is a schematic view of an apparatus for measuring the degree ofdouble refraction used in Examples.

FIG. 10 illustrates comparative Example 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be explained in detail below, referring tothe drawings.

FIG. 1 is a schematic view showing one embodiment of a process forpreparing a substrate for an optical disk according to the presentinvention.

In FIG. 1, numeral 1 is an extruder for melting and extruding resin, 2is a T-die for shaping the molten resin into a sheet form, 3 is a pressmolding part, consisting of three rollers 31, 32 and 33, where 32 is aroll stamper having a preformat pattern 6 on the surface, where thepreformat pattern corresponds to the stripy tracking grooves for anoptical card, and 31 and 33 are mirror surface rollers.

At first, resin pellets 4 charged into extruder 1 are heated and meltedin the extruder, compressed by a screw in the extruder, shaped into asheet form by the T-die and continuously extruded as a molten resinsheet 5. Then, the resin sheet 5 is pressed between the roller 31 andthe roller 32 and between the roller 32 and the roller 33, whereby thepreformat pattern 6 on the roller 32 is transferred onto the resin sheetto obtain a substrate 7 for an optical card in a sheet form having apreformat 8 with stripy tracking grooves 11 on the surface.

The present invention is characterized in that the extrusion direction Eof resin sheet 5 is in parallel to the direction of tracking grooves inthe stripe form of preformat 8. An optical card with less noise, whichis capable of suppressing occurrence of double refraction even if theoptical card is bent in the direction of tracking grooves during therecording and reproduction can be obtained from the substrate for anoptical disk, when the extrusion direction E of extruded and moldedthermoplastic resin sheet is in parallel to the direction of trackinggrooves in a stripe form.

In the present invention, preformat for an optical card formed on theresin sheet has stripy tracking grooves with a groove width of 0.1 to 5μm, a groove pitch of 1 to 12 μm and a groove depth of 0.01 to 0.4 μm,or further has prepits in the micron order, etc. besides the trackinggrooves.

Preformat 7 having the tracking grooves on the resin sheet in thepresent invention can be formed, for example, with a roll stampercoupled with molding of resin sheet, as shown in FIG. 1, or bytransferring a preformat pattern 6 onto the already extruded and moldedresin sheet 34 with a roll stamper 35 so that the extrusion direction Eof resin sheet may be in parallel to the direction of tracking groove,as shown in FIG. 3, or by transferring a preformat pattern onto theresin sheet with a flat stamper plate, or by forming a preformat 8 by 2Pprocess.

In view of the productivity of substrates for optical cards and lowercost of optical cards, the process shown in FIG. 1 is preferable,because molding of resin sheet and formation of preformat 8 can beconducted in one step.

The process shown in FIG. 1 will be further explained below.

According to the process shown in FIG. 1, the resin pellets 4 chargedinto the extruder 1 are heated and melted in the extruder, compressed bya screw in the extruder and shaped into a sheet form by a T-die. At thattime, the resin temperature is 260° to 330° C., preferably 280° to 320°C., for example, in the case of polycarbonate resin, and the resin iscontinuously extruded from the T-die as a clear molten resin sheet 5.T-die is so provided that the molten sheet can be extruded betweenrollers 31 and 32 in the press molding part 3. Distance between the tipend of T-die and rollers 31 and 32 is preferably not more than 100 mm soas to prevent solidification before the resin contacts the rollers. Theatmosphere temperature around the T-die and the rollers is preferably60° C. or higher.

Then, the resin sheet extruded between the rollers 31 and 32 is pressedbetween the heated roll-stamper 32 and press roller 33 to transfer thepreformat pattern 6. The roll-stamper 32 is kept at such a temperaturethat the resin may not solidify on the roll stamper. That is, rollstamper 32 is preferably heated to a temperature within a range of +20°to -20° C. of heat deformation temperature of the resin used. Forexample, in the case of polycarbonate resin, the surface temperature ofroll stamper is preferably heated to 100° C. to 160° C. That is, themolten resin sheet is not quenched in the above-mentioned temperaturerange and thus neither shrinkage nor deformation takes place on theresin sheet. The temperature of press roller 33 in the press moldingpart is preferably set to equal or somewhat lower than that of rollstamper 32.

Temperatures of these rollers are controlled, for example, by electricalheating through heaters cast in the rollers or by circulating a heatingmedium through the centers of rollers.

The thickness of resin sheet 7 for the substrate for an optical carddepends upon a clearance between rollers in the press molding part 3,degree of lip opening of T-die, and a difference between the extrusionspeed and the stretching speed, that is, degree of strething.

Roll stamper used in the molding process can be prepared, for example,by formation of a photoresist layer on a glass original plate,patterning with a laser beam or electron beam, development to form aresist pattern and then Ni-electroplating to obtain a thin Ni stamper.Then, the thin Ni stamper is fixed to a mirror surface-polished rollerroller base with an adhesive or jigs to obtain a roller form stamper. Apreformat pattern may be formed directly on a roller base or indirectlyon a pattern-forming layer provided on the surface of a roller base.

When preformat 8 on a substrate for an optical card has predeterminedsizes, that is, length A (in the pit writing direction) and width B(tracking groove-transverse direction), as shown in FIG. 4, thepreformat pattern 6 on the roll-staper has sizes, i.e. length acorresponding to the length A in the peripheral direction of rollstamper and width b corresponding to the width B in the directionperpendicular to the peripheral direction, and it is preferable to formthe preformat so that b/a is larger than B/A. That is, when thepreformat pattern 6 is transferred together with molding of resin sheet,shrinkage due to the cooling of resin sheet takes place and particularlylarger shrinkage takes place in the direction perpendicular to theextrusion direction of resin sheet, and consequently inexact sizes ofpreformat on the resin sheet are liable to be obtained. Particularly inthe present invention where the extrusion direction of the resin sheetis made in parallel to the direction of tracking grooves, the pitchbetween the tracking grooves is largely changed, resulting in occurrenceof a tracking error. However, by adjusting the sizes of preformatpattern on the roll stamper, as mentioned above, a difference between a'and A and a difference between b' and B can be made smaller and asubstrate for an optical card with small tracking error can be prepared,where a' is a length of format 8 formed on the resin sheet and b' is awidth thereof, as shown, for example, in FIG. 5. In FIG. 5, the pressroller 33 is shown by dotted lines to illustrate the preformat pattern 6on the roll stamper 32.

When the relationship between A and a and the relationship between B andb are made as given by the following equations (2) and (3), thedifference between a' and A and the difference between b' and B can bemade very small. Thus, this is very preferable. ##EQU1##

Furthermore, it is particularly preferable that the relationship betweenB and b satisfies the following equation (4). ##EQU2##

The thermoplastic resin material for the substrate according to thepresent invention can be any material that is amorphous andsubstantially optically isotropic, extrusion-moldable and transparent toa laser beam to be used, and includes, for example, polycarbonate,polystyrene, polyetherimide.

The substrate for an optical card in a sheet form prepared as above isthen cut into individual leaves, or a recording layer and a protectivelayer are formed on the substrate of a sheet form, to prepare opticalcards having a cross-section as shown in FIG. 6. FIG. 6 is across-sectional view in the grooves-transversing direction of trackinggrooves of an optical card according to the present invention, wherenumeral 61 is a recording layer, 62 an adhesive layer and 63 aprotective substrate.

For the recording layer 61 to be formed on the substrate, it ispreferable that the energy required for changing the reflectivity byirradiation of a recording energy beam is small. Furthermore, lesschange in reflectivity of the recorded parts (pits, etc.) and unrecordedparts by irradiation of a reproducing energy beam, is preferred. Amagnetic layer of Tb-Fe-Co or Gd-Fe-Co is used for these purposes.

Furthermore, an organic layer capable of changing optical properties byan energy beam can be continuously formed by applying a solution or adispersion and is suitable for mass production. For example,anthraquinone derivatives having indanthrene skeletons at the front andthe rear sides thereof, dioxazine compounds and their derivatives,triphenodithazine compounds, phenanthrene derivatives, cyaninecompounds, merocyanine comounds, pyrylium compounds, xanthene compounds,triphenylmethane compounds, croconium dyes, azo dyes, crocones, azines,indigoids, methine dyes, polymethine dyes, azulenes, squariumderivatives, sulfide dyes and metal dithiolate complexes can beenumerated.

An organic layer of any of the above-mentioned pigments can be formed byany well-known coating procedure, for example, dip coating, spraycoating, spinner coating, bar coating, roll coating, blade coating,curtain coating, etc. The thickness of the organic layer is generally500 to 2,000 Å, preferably about 1,000 Å.

In order to prevent the optical recording layer from deterioration byirradiation of a reproducing beam, a stabilizer can be added to any ofthese pigments. For example, the stabilizer is selected from thefollowing compounds in view of a compatibility with the pigment and asolvent. A few % by weight to 50% by weight of the stabilizer can beadded to the pigment on the basis of the pigment. When the amount of thestabilizer is too small, the effect as the stabilizer cannot beexpected, whereas, when more than 50% by weight of the stabilizer isadded, an absolute amount of heat-mode recording material is decreasedand a reduction in the sensitivity is observed. Thus, addition of 10% byweight to 30% by weight of the stabilizer to the pigment on the basis ofthe pigment is preferable. Particularly preferable is about 20% byweight because a high effect can be obtained without any reduction ofthe sensitivity.

The stabilizer includes, for example, various metal chelate compounds,particularly polydentate ligands having Zn, Cu, Ni, Cr, Co, Mn, Pd andZr as center metals, for example, tetradentate ligands such as N₄, N₂O₂, N₂ S₂, S₄, O₂ S₂, O₄, etc , or tridentate ligands such as N₂ O, NO₂,NS₂, O₃, NOS, etc. and other ligands such as water, ammonia, halogen,phosphine, amine, arsine, olefine, etc. or tetradentate type of twobidentate ligands such as N₂, NO, O₂, and S₂, furthermorebicyclopentadienyl ligands, cyclopentadienyl-tropylinium ligands, orcombinations thereof, and furthermore, various aromatic amines ordiamines, nitrogen-containing aromatic compounds and their onium salts,for example, aminium salts, diimonium salts, pyridinium salts,imidazoliniium salts, quinolinium salts, etc. Furthermore, pyryliumsalts, etc. as oxygen-containing aromatic salts may be used. Acombination of some of these stabilizers can be also used. A proportion(composition ratio) can be appropriately selected in view of thecoatability of pigment composition, stability of coating layer, opticalcharacteristics (reflectivity and transmissivity), recordingsensitivity, etc.

An adhesive for the adhesive layer 62 can be selected from a wide rangein order not to attach the recording layer due to the covering ofrecording layer 61. The adhesive for use in the adhesive layer includes,for example, vinyl acetate-based adhesives, vinylacryl acetate-basedadhesives, vinyl acetate copolymer-based adhesives, vinyl acetateemulsion-based adhesives, acrylic adhesives, acrylate-based adhesives,acrylic copolymer-based adhesives, ethylenic adhesives, ethylene-vinylacetae-based adhesives, ethylene-vinyl acetate copolymer-basedadhesives, polyethylene-based adhesives, methylene chloride-basedadhesives, polyamide-based adhesives, polyamide-amine-based adhesives,polyimide-based adhesives, urea-based adhesives, epoxy adhesives,epoxyurethane-based adhesives, epoxyacrylate-based adhesives, urethaneacrylate-based adhesives, polyester-based adhesives, chloroprene-basedadhesives, chloroprene rubber-based adhesives, nitrile-based adhesives,nitrile rubber-based adhesives, urethane-based adhesives,vinylurethane-based adhesives, polyurethane-based adhesives, olefinicadhesives, cyanoacrylate-based adhesives, alkyl acrylate-basedadhesives, vinylchloride-based adhesives, phenolic adhesives, SBR(styrene-butadiene rubber)-based adhesives, polyol-based adhesives,silica-alumina-based adhesives, synthetic rubber-based adhesives,emulsion-based adhesives, oligoester-based adhesives, cellulosicadhesives, formaldehyde-based adhesives, ultraviolet-curing typeadhesives, organic solvents, styrene-butadiene-freon TA-based adhesives,etc. Those which require such types of energy as heat, light, electronbeam, etc. for the adhesion are also effective unless the energydeteriorates the function of the optical recording material.

For the protective substrate 63, any material that can be used as theordinary card substrate is applicable in the present invention, andspecifically polyvinyl chloride, fluorine-substituted ethylene polymer,vinyl chloride-vinyl acetate copolymer, polyvinylidene chloride, acrylicpolymers such as polymethyl methacrylate, etc., polystyrene,polyvinylbutyral, acetylcellulose, styrene-butadiene copolymer,polyethylene, polypropylene, polycarbonate,epoxyacrylonitrite-butadiene-styrene copolymer, etc. can be used.

Sometimes, metal sheets of iron, stainless steel, aluminum, tin, copper,zinc, etc., synthetic paper, paper or fiber-reinforced plastics,compound materials of metal powder such as magnetic powder, etc. andplastics, ceramics can be widely used in view of the uses. It isneedless to say that those used in transparent substrates can be alsoemployed.

Apparatus for recording and reproducing information on an optical cardaccording to the present invention will be explained below, referring toFIG. 7.

The apparatus shown in FIG. 7 has both functions of recording andreproduction. At first, the recording mode of the apparatus will beexplained.

Data transmitted from a host computer are subjected to conversion ofparallel data to serial data, addition of error correction symbolsthereto, etc. by an optical card controller and then the serial data areconverted to code signals by a modulator circuit 71. Then, the dataconverted to the code signals are transmitted to a laser diode 21through a laser diode drive circuit 72 to be irradiated through asubstrate as a recording beam to a recording layer, thus the informationis recorded on an optical card. The optical card 10 reciprocally movesfacing to the recording beam by a driving means 26 and is bent by anoptical card bending means 27 at the same time to improve the flatnessof the recording beam-irradiated plane and further prevent the slippingof the optical card during the driving. By bending the optical card inparallel to the extrusion direction of the extrusion-moldedthermoplastic resin sheet used in the substrate for the optical card,substantially no double refraction occurs in the substrate for theoptical card, and exact pits without any spreading can be formed in therecording layer.

Reproduction mode of the apparatus shown in FIG. 7 will be explainedbelow.

In the reproduction mode, modulator and control systems 71 and 72 forthe laser diode are appropriately adjusted so as not to give anyfluctuation to the intensity of laser output. Output level from thelaser diode is set to a lower value than the necessary level for formingpits in the recording layer or reflecting layer of optical card 10.Then, the laser beam is focused on the recording layer surface orreflecting layer surface of the optical card 10 through PBS 22, QWP 23,a focusing lens 24 and the substrate 7. The light reflected on therecording layer surface or the reflecting layer surface passes againthrough QWP 23 and reflected on PBS 22 due to difference of polarizingplane from the incident light by 90° and enters an optical detector 25.

The intensity of light entering the optical detector 25 changes as thefocused beam passes over the pit parts of the recording layer or thereflecting layer.

Output of light detector 25 is amplified by an amplifier 73 and isconverted to reproduction signals and signals for the focusing servo andtracking servo by a matrix circuit 73. Then, the reproduction signaloutput from the matrix circuit is converted to digital signals by acomparator 74 and then clock signals are extracted therefrom by a PLLcircuit. The clock signals perform a synchronous demodulation ofreproduction signals in a data synchronous detecting system 75. Then,the synchronously demodulated reproduction signals are returned to theoriginal data by a reversed algorithm of the modulation in ademodulation circuit 76, and then transmitted to the optical cardcontroller to be read by the host computer.

In the reproduction mode, the optical card 10 is reciprocally moved withrespect to the reproducing beam by the driving means 26 and bent to aconvex form or a concave form with respect to the light source 21 by theoptical card-bending means 27 to improve the flatness of reproducinglight-reflected plane and prevent the slipping, etc. of the optical cardas in the recording mode. By bending the optical card in parallel to theextrusion direction of the extrusion-molded thermoplastic resin sheetused in the substrate for the optical card 10, substantially no doublerefraction occurs in the substrate for the optical card and consequentlythe reproducing light reflected on the recording layer or reflectinglayer will not generate noises on the light source due to passage of thereflected reproducing light through PBS, and reproduction of signal witha high S/N ratio can be obtained.

As explained above, the tracking grooves on the substrate for an opticalcard is molded in the parallel to the extrusion direction of the resinsheet, and an optical card prepared from the thus prepared substrate cankeep the occurrence of double refraction low and stable as the card isbent along the extrusion direction of the sheet during the recording andreproduction, and thus an optical card with a high key/N ratio, etc. canbe obtained.

Furthermore, a preformat of optical card, for example, tracking grooves,specifically those in a stripe form with a groove width of 3 μm andtrack pitch of 12 μm, is formed. Particularly the fluctuation of trackpitch is suppressed to a range of 12 μm ±0.1 μm, as set forth by thecode, and outside this range tracking errors frequently occur during therecording and reproduction.

Thus, in the formation of a preformt for an optical card with sizes of A× B, as shown in FIG. 4, changes in the dimensions of the preformat byshinkage of the sheet due to cooling after the extrusion-molding can beadjusted by making b/a larger than B/A, where a is the length in theperipheral direction of the preformat pattern on the roll stamper forthe transfer and b is the width in the direction perpendicular to theperipheral direction, as in the present invention, and thus substratesfor optical cards having an exact preformat can be mass-produced.

Furthermore, an optical card in a high C/N ratio with less trackingerror can be obtained according to the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention will be described in detail below, referring toExamples.

EXAMPLE 1

A substrate 7 for an optical card was prepared through a coat hungertype T-die 2, 20 cm wide, downwardly set to an extruder 1 with a screw,35 mm in diameter, as shown in FIG. 1. As resin, polycarbonate resin(Panlite L-1250, trademark of a product made by Teijin Kasei K.K.) wasused. A press molding section was composed of mirror surface-polishedrolls 31 and 33 and a roll stamper 32.

The resin extrusion conditions were such that barrel temperatures were300° C. at part a (Ta) of extruder 1, 300° C. at part b (Tb), 320° C. atpart c (Tc), and temperature of T-die 2 (Td) was 320° C. Under suchconditions, a molten resin sheet was formed, where the resin temperaturewas 280° C. to 320° C.

The roll stamper 32 was kept at 140° C., while the roll was kept at atemperature 1° to 2° C. lower than that of roll stamper 32, and the roll33 was kept at a temperature 20° to 21° C. higher than that of rollstamper 32.

A clearance between the lip of T-die and the press molding section wasset to 50 mm and the atmosphere from the point of resin sheet extrusionto the press molding section was controlled to 60° C. or higher byproviding a heating box around the passage of from the extrusion pointto the press molding section. Degree of lip opening of T-die was set to0.48 mm, and a gap between the roll 31 and the roll stamper 32 in thepress molding section was set to 0.4 mm. Under these conditions, apreformat pattern 6 on the roll stamper 32 was transferred onto a resinsheet 5 to mold a substrate for an optical card, 0.4 mm thick, with apreformat 8 composed of 2,583 tracking grooves at a pitch of 12 μm and atrack width of 3 μm, arranged in parallel to the extrusion direction E.

The thus obtained substrate for an optical card was subjected tomeasurement of double refraction of the substrate when the substrate wasmaintained in a flat plate state and also when the substrate was bent inparallel to the extrusion direction E of the resin sheet, as shown inFIG. 9. The results are shown in FIG. 8(A).

Measurement of double refraction was carried out with a measuringapparatus provided with a transmission type, circular polarized lightincident type optical system, as shown in FIG. 9, where numeral 91 is alaser diode, 92 a polarizer, 93 a collimator lens, 94 QWP, 95 ananalyzer and 96 a light detector. The wavelength of laser diode was setto 780 nm and the curvature d was set to 5 mm. The double refraction wasmeasured for the recording track shown by G in FIG. 8(B).

In the diagram shown in FIG. 8(A), the values obtained by the measuringapparatus for double refraction shown in FIG. 9 were plotted as two-foldvalues. In FIG. 8(A), 1 refers to the double refraction when thesubstrate was kept in a flat plate state and 2 refers to the doublerefraction when the substrate was bent.

Then, the surface on the preformat-having side of the substrate for anoptical card was coated with1,1,5,5-tetrakis(p-diethylaminophenyl)-1,3-pentadienyl perchlorate as apolymethine dye to a thickness of 1,000 Å, and a polycarbonate resinsheet having a thickness of 0.3 mm was attached thereon through a hotmelt adhesive sheet to obtain an optical card.

Then, the thus obtained optical card 10 was bent in the extrusiondirection of substrate 7 (d=5 mm), as shown in FIG. 7, and the opticalcard 10 was driven at 60 mm/sec with a driving means 26. Signal having afrequency of 100 KHz was recorded in the recording track G with arecording power of 3 mW, using a semiconductor laser having a wavelengthof 780 nm. Then, the recording track G was scanned with a semiconductorlaser power of 0.3 mW to reproduce the signal. C/N ratio of the signalobtained at that time is shown in Table 1.

COMPARATIVE EXAMPLE 1

A substrate 7 for an optical card of polycarbonate resin was prepared inthe same manner as in Example 1, except that the preformat having thetracking grooves was formed as inclined at 45° (θ=45°) to the extrusiondirection E, as shown in FIG. 10.

The thus prepared substrate for an optical card was subjected tomeasurement of double refraction in the same manner as in Example 1while keeping the substrate in a flat plate state. No substantial doublerefraction was observed as given by 1 in the diagram of FIG. 8A.

Then, the substrate for an optical card was bent in the paralleldirection to the tracking grooves, that is, in parallel to the directionof 45° inclination to the extrusion direction E to measure the doublerefraction in the same manner as in Example 1. It was so formed that thedouble refraction was increased as shown by 3 in the diagram of FIG.8(A).

Then, the substrate for an optical card was laminated with a recordinglayer and a protective layer in the same manner as in Example 1 toprepare an optical card. The thus prepared optical card was subjected torecording and reproduction of information in the same manner as inExample 1. C/N ratio obtained at that time is shown in Table 1.

COMPARATIVE EXAMPLE 2

A substrate 7 for an optical card polycarbonate resin was prepared inthe same manner as in Example 1. except that the tracking grooves wereformed as inclined at 90° (θ=90°).

The thus prepared substrate for an optical card was subjected tomeasurement of double refraction in the same manner as in Example 1while keeping the substrate in a flat plate state. No substantial doublerefraction was observed as given by 1 in the diagram of FIG. 8(A).

Then, the substrate for an optical card was bent in the directionparallel to the tracking grooves, that is, in the directionperpendicular to the extrusion direction to measure the doublerefraction in the same manner as in Example 1. It was found that thedouble refraction was increased as shown by 4 in the diagram of FIG.8(A).

Then, the substrate for an optical card was laminated with a recordinglayer and a protective layer in the same manner as in Example 1 toprepare an optical card. The thus prepared optical card was subjected torecording and reproduction of information in the same manner as inExample 1. C/N ratio obtained at that time is shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Recording and Reproducing Characteristics                                            Ex. 1     Comp. Ex. 1                                                                              Comp. Ex. 2                                       ______________________________________                                        C/N      51.2     dB     45.3  dB   47.2   dB                                 Carrier level                                                                          -20.6           -21.2      -20.5                                     Noise level                                                                            -71.8           -66.5      -67.7                                     ______________________________________                                    

As described above, the substrate for an optical card, when bent inparallel to the extrusion direction of resin sheet, does not cause muchincrease in the double refraction even by bending of the substrate, andhas no positional dependency and can produce an optical card havingcharacteristics excellent in recording and reproducing.

EXAMPLE 2

A substrate 7 for an optical card was prepared by using the sameapparatus as shown in FIG. 1 in the same manner as in Example 1, exceptthat as the roll stamper 32, a roll stamper having a preformat patternwith length a in the peripheral direction of the roll stamper and widthb in the direction perpendicular to the peripheral direction, as shownin FIG. 5, was used. The length a and width b of the preformat patterncorresponded to the predetermined length A and width B formed on thesubstrate for an optical card, respectively, as shown in FIG. 4.

In this Example, as the predetermined sizes of preformat formed on thesubstrate for an optical card, as shown in FIG. 4, the length A was setto 85.590 mm and the width B set to 30.990 mm, and 2,583 trackinggrooves were formed at equal intervals in parallel to the longitudinaldirection of the preformat with a tracking groove width of 3 μm and atracking groove depth of 3,000° Å in the area defined by A and B.

The length a of preformat pattern corresponding to the preformat was setto 85.848 mm and the width b set to 31.020 mm, and 2,583 groove patternscorresponding to the track grooves were formed at equal intervals inparallel to the longitudinal direction of the preformat pattern in thearea defined by a and b.

In the preformat 8 formed on the substrate for an optical card preparedby the roll stamper, the length was defined by a' and the width by b',as shown in FIG. 5, and a' and b' were measured to determine deviationsof a' and b' on the basis of the predetermined length A and thepredetermined width B of the preformat respectively.

An optical card was prepared by using the substrate in the same manneras in Example 1 and information was recorded on the optical card in thesame manner as in Example 1, and then 100 reproductions were repeated.The results are shown in Table 2.

EXAMPLES 3 to 5

Substrates 7 for optical cards were prepared in the same manner as inExample 2, except that the length a and the width b of the preformatpattern on the roll stamper 32 used in Example 2 was changed as shown inTable 2.

Deviations of the length a' and the width b' of preformat 8 formed onthe substrates for optical cards from the predetermined sizes A and B ofthe preformat for an optical card, respectively, as shown in Example 2were determined.

Optical cards were prepared by using the substrates in the same manneras in Example 2 to record information, and subjected to a repeatedreproduction test. The results are shown in Table 2.

COMPARATIVE EXAMPLE 3

A substrate for an optical card was prepared in the same manner as inExample 2, except that the length a and the width b of the preformatpattern on the roll stamper 32 were made equal to the predeterminedlength A and the predetermined width B of the optical card in Example 2.Deviations of the length a' and the width b' of preformat 8 formed onthe substrate for an optical card from the predetermined sizes A and Bof the preformat for an optical card, respectively, as shown in Example2, were determined.

An optical card was prepared by using the substrate in the same manneras in Example 2 to record information and subjected to a repeatedreproduction test. The results are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________                                 Deviations from the                                                                      Frequency                                        Sizes of preformat                                                                              predetermined sizes                                                                      of tracking                                      pattern on roll                                                                        Sizes of preformat                                                                     A and B of preformat                                                                     error                                            stamper (mm)                                                                           on substrate (mm)                                                                      (μm)    occurrence                            __________________________________________________________________________    Ex. 2                                                                         100x(a - A/A) = 0.1                                                                      a   85.848                                                                             a'  85.593                                                                             3          ⊚                      100x(b - B/B) = 0.3                                                                      b   31.020                                                                             b'  30.900                                                                             0                                                Ex. 3                                                                         0.15       a   85.931                                                                             a'  85.677                                                                             87         ∘                         0.40       b   31.036                                                                             b'  31.004                                                                             14                                               Ex. 4                                                                         0.05       a   85.677                                                                             a'  85.420                                                                             170        ∘                         0.10       b   31.005                                                                             b'  30.976                                                                             14                                               Ex. 5                                                                         0.07       a   85.803                                                                             a'  85.547                                                                             43         ⊚                      0.25       b   31.012                                                                             b'  30.980                                                                             10                                               Comp. Ex. 3                                                                   0          a   85.590                                                                             a'  85.333                                                                             257        X                                     0          b   30.990                                                                             b'  30.959                                                                             31                                               __________________________________________________________________________     ⊚: No occurrence of tracking error at all                      ∘: Substantially no occurrence of tracking error                  X: Frequent occurrence of tracking error                                 

What is claimed is:
 1. A process for preparing a substrate for anoptical card comprising molding tracking grooves in a stripe form on anextrusion-molded thermoplastic resin sheet by using a roll stamper sothat the extrusion direction of the thermoplastic resin sheet is madeparallel to the direction of the tracking grooves, whereina templatepattern corresponding to the tracking grooves is provided on theperipheral surface of the roll stamper and the stripe direction of thetemplate pattern is perpendicular to the axis of the roll stamper, and atrack pitch of the template pattern is larger than a track pitch of theoptical card which is set to avoid tracking errors.
 2. A process forproducing an optical card substrate in a sheet form, comprising formingtracking grooves in parallel lines on the surface of an extrusionmoldedthermoplastic resin sheet by using a roll stamper in a manner such thatthe extrusion direction of the thermoplastic resin sheet is parallel tothe direction of the tracking grooves, whereina template pattern havinga width b along a stamper axis corresponding to tracking grooves isprovided on the peripheral surface of the roll stamper and the stripedirection of the template pattern is perpendicular to the axis of theroll stamper, and said width 6 of the template pattern is larger thanwidth b' of a preformat of the optical card having a given number oftracking grooves and a tracking pitch which is set to avoid trackingerrors.
 3. A roll stamper comprising an axis and a peripheral surface onwhich a template pattern of parallel lines corresponding to trackinggrooves of an optical card is provided, for forming the tracking grooveonto a resin sheet in succession to molding the resin sheet into theoptical card substrate sheet, whereinthe template pattern of parallellines corresponding to tracking grooves are provided in a direction thatthe parallel lines are perpendicular to the axis of the roll stamper,and a track pitch of the template pattern is larger than a track pitchof an optical card which is set to avoid tracking errors.
 4. A rollstamper having a template pattern on a peripheral surface thereof, forforming a preformat pattern of a predetermined number of trackinggrooves of parallel lines on a resin sheet, whereinthe template patternof parallel lines having a width b along a stamper axis corresponding totracking grooves are provided in a direction that the parallel lines areperpendicular to the axis of the roll stamper, and said width 1 of thetemplate pattern is larger than a width b' of the preformat of theoptical card having a predetermined number of tracking grooves and atracking pitch which is set to avoid tracking errors.
 5. An apparatusfor continuous production of an optical card substrate in a sheet form,forming tracking grooves in parallel lines on the surface of anextrusion-mold thermoplastic resin sheet in a manner that the extrusiondirection of the thermoplastic resin sheet is parallel to the directionof the tracking grooves, comprising a roll stamper having a templatepattern of parallel lines corresponding to said tracking grooves on itsperipheral surface, whereinthe direction of the template lines isperpendicular to the axis of the roll stamper and a track pitch of thetempalte pattern is larger than a track pitch of the optical card whichis set to avoid tracking errors.
 6. An apparatus for continuousproduction of an optical card substrate in a sheet form, forming apreformat tracking grooves of parallel lines on the surface of anextrusion-molded thermoplastic resin sheet in a manner that theextrusion direction of the thermoplastic resin sheet is parallel to thedirection of the tracking grooves, comprising a template pattern ofparallel lines having a width b along a stamper axis corresponding totracking grooves is provided on the peripheral surface of the rollstamper whereinthe line direction of the template pattern isperpendicular to the axis of the roll stamper, and said width b of thetemplate pattern is larger than the a width b' of the preformat of theoptical card having a predetermined number of tracking grooves and atracking pitch which is set to avoid tracking errors.